Preheat the oven to 325 degrees and sanitize 4 1/2-pint canning jars. Running the jars through the dishwasher is fine. Grease the jars with butter.
In a stand mixer or blender, combine the wet ingredients. Add the salt and flour, and combine thoroughly.
Divide the batter evenly among the four jars. Add 1/4 cup of berries to each jar, reserving half a cup of berries for garnish.
Fill a large casserole dish or high-sided roasting pan 3/4 full with hot water. Carefully place the jars in the hot water. The water should cover the bottom 3/4 of each jar.
Carefully put the casserole dish in the oven. (This can be precarious. You don't want the jars to tip over or all is lost.)
Bake for 60 to 75 minutes, until the clafoutis are set (no longer watery).
Remove the jars from the water bath and cool them for at least 10 minutes. Top with the remaining berries and serve warm. Alternately, you can refrigerate the cooled clafoutis and serve cold. A dollop of whipped cream or sweetened Greek yogurt is a nice finishing touch.